Put the sugar, water, and corn syrup in a medium pot. Heat over medium high heat and cook, without stirring, until the sugar mixture is straw (hay) colored, approximately 8 minutes.
Reduce the heat to low. Continue to cook, without stirring, until the caramel is amber colored. Swirl the pan every few minutes while cooking on low. The caramel will be 360-370 degrees F.
Remove the pot from the heat. Add the heavy cream, vanilla, salt, and whiskey.
The mixture will bubble, steam, and feel like a hard block of sugar is in the pot. Stir until the sauce is smooth and the hard sugar dissolves.
Let the caramel cool slightly. It can be stored in the refrigerator for up to 2 weeks. Reheat gently in small intervals as needed to make it pourable again.